Many aircraft gas turbine engines are supplied with lubricant from a pump driven lubrication supply system. In particular, the lubrication supply pump, which may be part of a pump assembly having a plurality of pumps on a common, engine-driven shaft, draws lubricant from a lubricant reservoir, and increases the pressure of the lubricant. The lubricant is then delivered, via an appropriate piping circuit, to the engine. The lubricant is directed, via appropriate flow circuits within the engine, to the various components that may need lubrication, and is collected in one or more recovery sumps in the engine. One or more of the pump assembly pumps then draws the lubricant that collects in the recovery sumps and returns the lubricant back to the reservoir.
When an aircraft gas turbine engine is shutdown, the lubricant is typically removed and returned to the reservoir. In many instances this is accomplished by actuating a valve that, when appropriately positioned, allows the engine-driven pump to draw air, rather than lubricant, into the system. The pump directs the air into the engine, displacing the lubricant therefrom, and directing the displaced lubricant back to the lubricant reservoir. Because the engine is being shutdown, the inertia of the engine main rotating group supplies the rotational drive force to the engine-driven pump to provide adequate pump speed and air flow through the piping circuit to thoroughly displace the lubricant from the engine.
Although engine-driven pumps are generally reliable and robust, many lubrication supply systems are being designed and implemented with electric motor-driven pumps. Thus, instead of being mechanically driven by a gas turbine engine, the pumps are driven by electrical motors, which are energized from an electrical power bus. The electrical power bus is, in many instances, energized via an electrical machine that is driven by the engine.
Hence, there is a need for an aircraft engine lubricant supply system that includes an electric motor-driven pump that can adequately displace the lubricant in a gas turbine engine during the engine shutdown sequence. The present invention addresses at least this need.